An Iranian oil tanker at the heart of a dispute between the US and Tehran was photographed off the Syrian port of Tartus, after going dark earlier in the week.

A US space technology company, Maxar Technologies Inc, shared a photo showing the tanker Adrian Darya 1 very close to Tartus on 6 September.

The ship appeared to have turned off its transponder in the Mediterranean west of Syria, Refinitiv ship-tracking data showed on Tuesday.

Two sources also told MEE on Friday that oil from the Adrian Darya 1 had been offloaded to a port in the country.

One said that 55 percent of the ship's cargo, previously reported as 2.1 million barrels of oil, had been unloaded by 10.15pm local time (7.15pm GMT) on Thursday night.

The tanker, which is loaded with Iranian crude oil, sent its last signal giving its position between Cyprus and Syria sailing north at 15:53 GMT on Monday, the data showed.

The staunchly anti-Iran US National Security Advisor John Bolton tweeted the satellite images on Saturday morning, claiming: "Tehran thinks it's more important to fund the murderous Assad regime than provide for its own people."

The vessel, formerly named Grace 1, was detained by British Royal Marine commandos off Gibraltar on 4 July as it was suspected to be en route to Syria in violation of European Union sanctions.

Two weeks later, Iran in retaliation seized a British-flagged tanker in the Strait of Hormuz leading into the Gulf.

Gibraltar released the Iranian vessel on 15 August after receiving formal written assurances from Tehran that the ship would not discharge its 2.1 million barrels of oil in Syria.

However, shipping sources say the tanker is likely to try to conduct a ship-to-ship transfer with another vessel for part of its cargo after Iran said a sale had been concluded.

Washington has warned any state against assisting the ship, saying it would consider that support for a terrorist organisation, namely, Iran's Islamic Revolutionary Guard Corps.

The US Treasury Department blacklisted the tanker on Friday.

Iran seizes ship for 'smuggling fuel'

Iran's semi-official news agency ISNA reported on Saturday that Iran's coast guard had seized a vessel for allegedly smuggling fuel in the Gulf and detained its 12 crew members from the Philippines.

The vessel was carrying nearly 284,000 litres of diesel, the news agency said on Saturday.

Iran, which has some of the world's cheapest fuel prices due to heavy state subsidies and the fall of its currency, has been fighting rampant fuel smuggling by land to neighbouring countries and by sea to Gulf Arab states.

It has frequently seized boats it says are being used for smuggling oil in the Gulf.